The present invention relates to an innovatory armchair structure of the type provided with a base seat, a back and, optionally, a footrest, which elements are movable through electric motors.
Well known in the art are armchairs having a footrest and a back adapted to be drivingly inclined by means of electric motors.
Motors mounted on the fixed frame of the armchair have one rotation shaft close to the back and the other close to the footrest. Crank mechanisms connect each rotation shaft to the respective element (back or footrest) to be moved.
Usually, the rear shaft controls movement of the back, whereas the front shaft simultaneously controls movement of the footrest and the base seat, in terms of lifting the base seat (pivotally mounted, at the back, to the fixed frame) at the front, as the footrest itself moves upwardly.
For movement transmission, kinematic connecting rod-crank mechanisms connect the rear shaft to the back and the front shaft to the footrest and the base seat.
This structure is rather complicated, relatively expensive and bulky.
In addition, the inclination movement of the base seat should have to be used for maintaining a given angle between the bust and the pelvis when the back is greatly inclined. However, since the base seat movement is only connected to the footrest movement, this effect cannot be reached if the footrest is left at its lowered position or at all events it is not completely raised. But, when the footrest is even only partly lowered there is the maximum requirement of keeping an angle between the seat base and the back for avoiding too much stress at the lumbar region.
In the opposite case too, if the footrest is wished to be raised leaving the back at its completely lifted position, too much stress may be caused at the lumbar region. In fact, since the base seat movement is connected to the footrest movement, by raising the footrest, the angle between the base seat and the back is simultaneously reduced. If the back is completely raised, this angle may become too small for a comfortable position.
A further undesirable effect present in the above-mentioned known art is that of having a distance between the front shaft and the footrest which increases on increasing of the base seat inclination, because the footrest is hinged on the front edge of the base seat and moves therewith, whereas the motor is fixed to the ground. As a result, the driving shaft must have a relatively high rotation angle for completely raising the footrest, so as to compensate for the progressive moving away of the hinging points of the kinematic connecting rod-crank transmission mechanism between the driving shaft and the footrest.  less than Kinematic connections are known also by DE-A-33 16 533, wherein a chair is provided with a spring to damp the downward movement of the seat, and by U.S. Pat. No. 3,936,929, showing a dental chair whose seat is pivotally connected to the support frame at the rear end, so as to tilt up the seat when the backrest is lowered. greater than 
It is a general object of the present invention to eliminate the above mentioned drawbacks by providing a power-driven armchair having an innovatory kinematic movement structure.
In view of the above object, in accordance with the invention, an armchair structure has been devised in which the base seat is pivotally mounted, at the front, on the support frame according to a first transverse axis, on said base seat being pivotally mounted the back, at the rear, according to a second transverse axis for rotation of the back itself, the back having extensions extending downwardly past said second axis and having ends constrained to slide longitudinally of the armchair, power-driven means controlling rotation of the back about said second axis, so that on rotation of the back about said second axis, the base seat rotates in the same way about said first axis.